I went along to be enlightened and came away consumed with despair at the political realities which oblige arts managers to give up a working day for a preach-in on multiculturalism. The symposium was called Cultural Diversity and the Classical Music Industry and it yammered on all day yesterday in a dreary side-room at the Royal Festival Hall, overlooking the railway cuttings. There was a sell-out attendance from just about every classical body in Britain bigger than a string quartet. This might make you think that the theme was compulsive.

Compulsory is more like it. As things stand in British arts, only an autist would dare to profess disinterest in diversity. With 7.9 percent of the population derived from ethnic minorities and the government sloganising away about inclusion, it would have been a brave orchestral boss who stayed away from diversity day. One manager whispered to me that his absence would surely have been noted.

There was an ominous edge to the proceedings. The organising body, the Association of British Orchestras (ABO), had aligned the event with the objectives of Arts Council England - specifically with the ACEs aim to make cultural diversity central to all that it undertakes. The ACE sent no fewer than ten observers to a room holding 160. An awful lot of next years funding must hinge on diversity compliance.

As for sell-outs, that was the fundamental premise. The ABO, representing a dwindling and dangerously uncool sector, was waving a white flag of acceptance that art must, for the time being, take second place to social engineering. Orchestras are increasingly expected to hire audience development managers and work with grassroots communities if they want to carry on playing the symphonies of Beethoven and Brahms.

The day began combatively with a speech from Lord Moser, once chairman of the Royal Opera House and now of the British Museum Development Trust. Lord Moser, 81, told the apparatchiks that orchestras do not deserve lectures or pressures from the arts councils  what is lacking is on the other side of the coin, in the education and funding systems.

The reason orchestras have so few non-white players  only two, for instance, in the City of Birmingham Symphony Orchestra in the heart of multicultural Midlands  is because music teaching has been neglected in the poorest areas. State school recruitment of music teachers was down 12 percent nationally last year. Most of those teaching music in secondary schools were, he said, untrained in music. Until they provide music teaching for minority children, the authorities cannot point a finger at orchestras for failing to engage non-whites as players, staff and audiences. Classical music will always be a minority interest, asserted Lord Moser, but it should not be as much of a minority as it has been allowed to become in this country.

After that, it was all downhill as the diversity industry turned its rage on the orchestral craft. Professor Lola Young, head of culture at the Greater London Authority and previously chair of the ACEs diversity panel, said we must change the look of the classical music industry. The professor, resplendent in an African-style headwrap, named George Augustus Bridgewater, the black violinist for whom Beethoven wrote his Kreutzer Sonata, as a useful role model. Every classical buff in the room knew the name was Bridgetower, but they were too cowed to correct a dominatrix of political correctness.

Kim Evans, executive director of arts at the ACE, argued that if diversity was good for business, it must be twice as good for art. We are asking you to use your funding in different ways, she instructed, to approach audiences in different ways. A chill set in as she drew parallels with the ACEs assault on the theatrical sector, which it condemned as institutionally racist and then promised to help reform. Evans urged orchestras to develop positive action plans before they were similarly sin-binned.

Roger Wright, head of Radio 3 which is getting flak from classic lovers for its output of world music, confessed that everyone at the BBC now undergoes diversity training. Roger Lewis, head of easy-listening Classic FM, exhorted us, perhaps ironically to get out of comfort zones.

And so it went on, a daylong drizzle of ambiguities, hypocrisies and dissimulations that could not conceal a grim inevitability. Diversity, or the policy that speaks its name, is a means of diverting orchestras from what they ought to be doing, making music, to what the Government ought to be doing, creating social harmony.

Few rose to challenge its preposterousness. Diversity is, to most of us, a fact of life. One does not have to travel far these days to find a cafe serving braised ostrich, or look beyond the next street corner to realise that forced marriages, honour killings and female circumcision exist in our midst. There are bright and dark aspects to the mass immigration of the past 30 years.

The cultural benefits are, however, overwhelmingly heartening. The literature, art and music of this country have been enriched beyond measure by a generation of inter-mingling on equal terms with other traditions. London in particular has become the hub of cross-cultural fertilisation as Paris was between the wars and New York briefly afterwards. Such melting-pots are made by mutual respect. No-one wants qawwali ensembles to doff caps and sing Haydn any more than a symphony orchestra should have to drop oboes and bang dustbin lids.

Yet that is what the diversity peddlers are pushing. Orchestras which struggle against an already inhospitable zeitgeist are being told to change their ways, while immigrant cultures are celebrated for their supposed purity. It is absurd, unfair and inherently disastrous.

Sitting amid the Blairite blather, I was transported back to the notorious Zhdanovitsa of 1948, when Soviet composers were summoned to Leningrad to be instructed by party hacks, on pain of exile, on how to write music for the new society. There was something of that fear on the South Bank yesterday.

And an uglier precedent sprang to mind. The ACEs aim is to accelerate the integration of minorities into established arts, heedless of cultural consequences. It amounts to a mirror image of Hitlerite policy which entailed the removal of non-aryan races from German music, even though this would relegate the art to the margins of civilisation.

That one policy is well-intentioned and the other unutterably evil is immaterial. What the world learned from Stalin and Hitler is that state organs have no business meddling with culture. That lesson is being obliterated in Britain where cultural diversity is brandished as a weapon to intimidate the performing arts and ultimately to emasculate them.